The objective of this study is to determine whether endogenous growth hormone (GH) regulates carbohydrate metabolism in normal animals by modulating sensitivity to insulin and by direct effects on peripheral carbohydrate utilization. To pinpoint the specific contribution of GH to carbohydrate homeostasis in animals with intact endocrine function, antibodies to rat GH (ArGH) will be administered to normal rats to neutralize their endogenous GH. The acute metabolic consequences of isolated GH deficiency will be followed. The effectiveness of ArGH treatment in neutralizing the activity of endogenous GH will be tested biologically and immunologically. Representative aspects of carbohydrate, lipid and protein metabolism will be measured on serial plasma samples obtained via indwelling cannulas, and in tissues taken from the animals at the end of treatment. Glucose tolerance tests will be performed to assess peripheral glucose utilization and insulin secretion in GH deficiency. Responses to administered insulin will be measured in vivo. Since compensatory changes can occur in normal rats treated with ArGH, glucose utilization and insulin sensitivity will also be tested directly in adipose tissue and muscle. Rapid metabolic changes accompanying ArGH treatment will provide information on the role of endogenous GH in the moment-to-moment regulation of carbohydrate metabolism. This animal model will then be used to identify possible mediators of the actions of GH, to study relationships between the effects of GH and glucocorticoids on insulin sensitivity and glucose utilization, and to determine the role of endogenous GH in altered metabolic states such as diabetes mellitus and fasting.